A laser tracker for continuous tracking of a reflecting target and for determining the distance to the target is provided. The laser tracker may include a base defining a standing axis, a beam steering unit for emission of a measuring radiation and for receiving at least a part of the measuring radiation reflected by the target. The beam steering unit is motorized to be pivotable relative to the base around the standing axis and a tilt axis extending substantially orthogonal to the standing axis. Furthermore, the tracker has a distance measuring unit configured as an interferometer for determining a change in distance to the target by means of interferometry, an interferometer laser beam source for generating the measuring radiation for the interferometer and an angle measurement functionality for determining an alignment of the beam steering unit relative to the base. The interferometer laser beam source may be configured as a laser diode.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A laser tracker for continuously tracking a reflective target and for determining distance with respect to the target comprising: a base defining a vertical axis; a beam directing unit for emitting a measurement radiation and for receiving at least one part of the measurement radiation reflected at the target, wherein the beam directing unit is pivotable in motorized fashion about the vertical axis and an inclination axis, which is substantially orthogonal with respect to the vertical axis, relative to the base; a distance measuring unit embodied as an interferometer and serving for determining a change in distance with respect to the target by means of interferometry; an interferometer laser beam source for generating the measurement radiation for the interferometer; and an angle measuring functionality for determining an orientation of the beam directing unit relative to the base; wherein the interferometer laser beam source is embodied as a laser diode and the laser diode has a wavelength-selective component arranged in such a way that the measurement radiation is configured to be generated in longitudinally monomode fashion with a defined emission wavelength and with a coherence length of at least 10 m, wherein the coherence length of at least 10 m is configured to be determined by means of the interferometer.
2. The laser tracker according to claim 1 , wherein: the laser diode has a first resonator unit, which defines a number of laser modes which arise jointly, the wavelength-selective component is embodied in such a way that it acts as a second resonator unit to extract a principal laser mode from the number of laser modes by means of an interaction of the wavelength-selective component with the laser diode, and a diode radiation is configured to be emitted as longitudinally monomode measurement radiation having only the principal laser mode, such that the emission wavelength and the coherence length of the measurement radiation are defined, wherein the wavelength-selective component is embodied as an optical grating.
3. The laser tracker according to claim 1 , wherein the laser diode is embodied as laser selected from the list consisting of: a distributed feedback laser, a distributed Bragg reflector laser, a fiber Bragg grating laser, an external cavity diode laser, a diode pumped solid state laser, a discrete mode laser, and a microchip laser.
4. The laser tracker according to claim 1 , wherein the emission wavelength of the measurement radiation is between 600 nm and 700 nm.
5. The laser tracker according to claim 1 , wherein the laser tracker has a control unit, and the laser diode is embodied in such a way that the emission wavelength of the measurement radiation is variable in longitudinally monomode fashion within a specific emission wavelength range, wherein the emission wavelength is variable in a manner controlled by the control unit as a result of a change in the temperature of the laser diode and/or a change in an electric current present at the laser diode.
6. The laser tracker according to claim 5 , wherein the laser diode is configured to be driven by means of the control unit in such a way that an emission power of the measurement radiation is variable.
7. The laser tracker according to claim 1 , wherein the laser tracker has a wavelength stabilization unit for stabilizing the measurement radiation generated by the laser diode, such that the emission wavelength is present continuously within a defined wavelength range, wherein the wavelength stabilization unit is embodied as an absorption cell, wherein the laser tracker has an optical connecting fiber for connecting the wavelength stabilization unit to the interferometer laser beam source.
8. The laser tracker according to claim 1 , wherein the laser tracker has at least one optical fiber, wherein the measurement radiation is configured to be guided by means of the optical fiber to the interferometer, wherein the measurement radiation generated by the laser diode is coupled into the optical fiber.
9. The laser tracker according to claim 1 , wherein the measurement radiation is configured to be coupled into the beam directing unit by means of an optical fiber.
10. The laser tracker according to claim 1 , wherein the laser tracker has a support pivotable about the vertical axis relative to the base.
11. The laser tracker according to claim 1 , wherein the laser tracker additionally has an absolute distance measuring unit for determining a distance with respect to the target, according to the principle of time-of-flight measurement and/or according to the phase measurement principle and/or according to the Fizeau principle.
12. The laser tracker as claimed in claim 11 , wherein a precision distance with respect to the target is configured to be determined in a manner dependent on the distance determined by means of the absolute distance measuring unit and the change in distance determined by means of the distance measuring unit.
13. The laser tracker according to claim 1 , wherein the emission wavelength of the measurement radiation is between 630 nm and 635 nm.
14. The laser tracker according to claim 1 , wherein the emission wavelength of the measurement radiation is between 850 nm and 900 nm.
15. The laser tracker according to claim 1 , wherein the emission wavelength of the measurement radiation is between 850 nm and 855 nm.
16. The laser tracker according to claim 1 , wherein the emission wavelength of the measurement radiation is between 892 nm and 896 nm.
17. A distance measuring unit, comprising: a laser diode designed for generating a longitudinally monomode measurement radiation with: a defined emission wavelength; and a coherence length of at least 10 m; wherein the distance measuring unit is embodied as an interferometer of a laser tracker for determining a change in distance with respect to a target by interferometry by means of the measurement radiation generated by the laser diode.
18. A method for determining a change in distance with respect to a target by means of interferometry with a laser tracker, wherein the laser tracker includes: a base defining a vertical axis, a beam directing unit for emitting a measurement radiation and for receiving at least one part of the measurement radiation reflected at the target, wherein the beam directing unit is pivotable in motorized fashion about the vertical axis and an inclination axis, which is substantially orthogonal with respect to the vertical axis, relative to the base, a distance measuring unit embodied as an interferometer and serving for determining a change in distance with respect to the target by means of interferometry, and an interferometer laser beam source for generating the measurement radiation for the interferometer, and wherein the method comprises: emitting the measurement radiation, receiving the at least one part of the measurement radiation reflected at the target, and determining the relative distance, wherein the interferometer laser beam source is embodied as a laser diode and the laser diode has a wavelength-selective component arranged in such a way that the measurement radiation is generated in longitudinally monomode fashion with a defined emission wavelength and with a coherence length of at least 10 m.
19. The method as claimed in claim 18 , wherein the measurement radiation generated by the laser diode is stabilized in such a way that the emission wavelength is present continuously within a defined wavelength range.
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November 2, 2012
July 26, 2016
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